Method for producing hollow fine particle, and hollow fine particle

Abstract

To provide a solution of a problem of making a hole number and a volume fraction of a hollow fine particle more constant in production of a hollow fine particle, and a solution of a problem of increasing kinds of polymers that can be used by way of no polymerization reaction.SOLUTION: A method for producing a hollow fine particle pertaining to the present disclosure includes: (1) a process of emulsifying a polymer solution in an aqueous solution containing a surface active agent to obtain an emulsion; and (2) a process of drying the emulsion obtained in the process (1) to obtain a hollow fine particle, where the polymer solution includes at least one solvent (A) having a logP or ClogP of 0.5 or higher; at least one solvent (B) having a boiling point higher than that of the solvent (A); and at least one polymer (C) soluble to the solvent (A).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing hollow microparticles and hollow microparticles. [Background technology]

[0002] The following method for producing hollow fine particles is exemplified as a conventional technique: Patent Document 1 discloses a production method consisting of the following three steps. First step: An aqueous solution containing a surfactant is prepared. Second step: A solution in which a resin precursor is dissolved in a solvent to a concentration of 40% by weight or less is dispersed in the aqueous solution of step 1 in which a surfactant has been dissolved, and then the solution is promptly diluted with water. Third step: The solvent is removed and the precursor is polymerized to form hollow resin particles.

[0003] Patent Document 2 discloses a manufacturing method comprising the following steps: a step of dispersing encapsulated microparticles in an aqueous solution containing a microparticle-forming substance to form a dispersed phase, a step of releasing droplets of the dispersed phase into a lipophilic continuous phase through a membrane member having a predetermined pore size to form a water-in-oil emulsion, a step of adding a crosslinking agent to the water-in-oil emulsion to crosslink the microparticle-forming substance to form microparticles containing encapsulated microparticles, and a step of introducing the encapsulated microparticle-containing microparticles into a solvent capable of dissolving the encapsulated microparticles to form hollow microparticles having at least one hollow hole and an average particle size of 0.1 μm to 10 μm.

[0004] Patent Document 3 discloses a method for producing hollow microparticles containing a fluorine-containing resin, which comprises the steps of dispersing a solution containing a fluorine-containing monomer, an oil-soluble initiator, and a non-polymerizable solvent in water containing a fluorine-containing surfactant, and polymerizing the fluorine-containing monomer to obtain hollow microparticles. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-263553 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-214219 [Patent Document 3] JP 2020-183500 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional methods for producing hollow microparticles have the following problems: First, the methods for producing hollow microparticles described in Patent Documents 1 and 3 require a polymerization reaction of a monomer, which poses a problem that polymers that cannot be polymerized in a dispersion medium cannot be used.

[0007] Furthermore, in the manufacturing method of Patent Document 2, the core part of the core-shell structure obtained as an intermediate is solid, making it difficult to control the number of pores. Specifically, since the number of core particles incorporated into the polymerization solvent microparticles containing the core material etc. cannot be controlled, the shape, number of pores, volume fraction, and film thickness are not constant, making it difficult to achieve stable performance. [Means for solving the problem]

[0008] [1] (1) (A) at least one solvent having a logP or ClogP of 0.5 or greater; (B) at least one solvent having a boiling point higher than that of said solvent (A); and (C) at least one polymer soluble in said solvent (A); a step of emulsifying a polymer solution containing the polymer in an aqueous solution containing a surfactant to obtain an emulsion; and (2) A step of obtaining hollow microparticles by removing the dispersion medium and the solvent (B) from the emulsion obtained in the step (1). A method for producing hollow microparticles, comprising:

[0009] [2] The method for producing hollow microparticles according to [1], wherein in the step (2), hollow microparticles are obtained via a core-shell structure in which the solvent (B) is contained in the core and the polymer (C) is contained in the shell.

[0010] [3] The method for producing hollow microparticles according to [1] or [2], wherein in the step (2), the dispersion medium and the solvent (B) are removed by freeze-drying, heat drying, or vacuum drying.

[0011] [4] The main chain of the polymer (C) is: one or more groups selected from the group consisting of siloxane, amide, imide, ester, ether, sulfonyl, sulfone, and ketone; or Ring structure The method for producing hollow microparticles according to any one of [1] to [3], comprising:

[0012] [5] The method for producing hollow microparticles according to any one of [1] to [4], wherein the polymer (C) is at least one polymer selected from the group consisting of polydialkylsiloxane, polyphenylene ether, polyamide, polyetherimide, polyimide, polyamideimide, polyester, polycarbonate, polyacetal, polyaryletherketone, polysulfone, polyethersulfone, and cycloolefin polymer.

[0013] [6] The method for producing hollow microparticles according to any one of [1] to [5], wherein the polymer (C) is polydimethylsiloxane or polyimide.

[0014] [7] The method for producing hollow microparticles according to any one of [1] to [6], wherein the boiling point of the solvent (A) at room temperature and normal pressure is 100° C. or lower.

[0015] [8] The method for producing hollow microparticles according to any one of [1] to [7], wherein the solvent (A) has a logP or ClogP of 1 to 3.

[0016] [9] The method for producing hollow microparticles according to any one of [1] to [8], wherein the solvent (A) is at least one solvent selected from the group consisting of fluoroethers, chloroform, and dichloromethane.

[0017]

[10] The method for producing hollow microparticles according to any one of [1] to [9], wherein the solvent (B) is a perfluorocarbon.

[0018]

[11] Hollow microparticles, the shell of which contains a polymer that is soluble in a solvent having a logP or ClogP of 0.5 or more.

[0019]

[12] The main chain of the polymer is: one or more groups selected from the group consisting of amide, imide, ester, ether, sulfonyl, sulfone, and ketone; or Ring structure The hollow microparticle according to

[11] , comprising:

[0020]

[13] The hollow microparticle according to

[11] or

[12] , wherein the polymer is at least one polymer selected from the group consisting of polydialkylsiloxane, polyphenylene ether, polyamide, polyetherimide, polyimide, polyamideimide, polyester, polycarbonate, polyacetal, polyaryletherketone, polysulfone, polyethersulfone, and cycloolefin polymer.

[0021]

[14] The hollow microparticle according to any one of

[11] to

[13] , wherein the polymer is at least one polymer selected from the group consisting of polyester, polyamide, polyamideimide, polyimide, polyetherimide, and polycarbonate.

[0022]

[15] The hollow microparticle according to any one of

[11] to

[14] , wherein the polymer is polydimethylsiloxane or polyimide.

[0023]

[16] The hollow microparticles according to any one of

[11] to

[15] , wherein the boiling point of the solvent at room temperature and normal pressure is 100° C. or lower.

[0024]

[17] The hollow microparticles according to any one of

[11] to

[16] , wherein the solvent has a logP or ClogP of 1 to 3.

[0025]

[18] The hollow microparticles according to any one of

[11] to

[17] , wherein the solvent is at least one solvent selected from the group consisting of fluoroethers, chloroform, and dichloromethane.

[0026]

[19] The hollow microparticles according to any one of

[11] to

[18] , which have an average particle diameter of 1 μm to 50 μm.

[0027]

[20] The hollow microparticle according to any one of

[11] to

[19] , wherein the shell has a thickness of 0.01 μm to 20 μm.

[0028]

[21] The hollow microparticle according to any one of

[11] to

[20] , wherein the volume fraction of the shell layer constituting the particle is 50% or less.

[0029]

[22] The hollow microparticle according to any one of

[11] to

[21] , wherein the number of voids in the particle is 1 or 2.

[0030]

[23] On the surface and inside of the shell and in the core, in total: (A) at least one solvent having a logP or ClogP of 0.5 or greater; and / or (B) at least one solvent having a boiling point higher than that of the solvent (A); The hollow microparticles according to any one of

[11] to

[23] , wherein the total amount of the above is 0% by weight to 1% by weight. [Effects of the Invention]

[0031] The present disclosure provides a method for producing hollow microparticles that solves the above-mentioned problems, making it easier to control the volume fraction and film thickness of the shell layer compared to conventional techniques, and also enabling the use of a wider variety of polymers compared to conventional techniques. DETAILED DESCRIPTION OF THE INVENTION

[0032] While one embodiment of the present disclosure will be described in detail below, the scope of the present disclosure is not limited to the embodiment described here, and various modifications can be made without departing from the spirit of the present disclosure. Furthermore, when multiple upper and lower limit values ​​are listed for a specific parameter, any of these upper and lower limit values ​​can be combined to form a suitable numerical range.

[0033] Method for producing hollow microparticles In the present disclosure, "hollow microparticles" refer to particles having pores inside that are not connected to the outside. The pores may or may not be spherical in shape. The number of pores may be one or more.

[0034] The method for producing hollow microparticles according to the present disclosure includes: (1) (A) at least one solvent having a logP or ClogP of 0.5 or greater; (B) at least one solvent having a boiling point higher than that of said solvent (A); and (C) at least one polymer soluble in said solvent (A); a step of emulsifying a polymer solution containing the polymer in an aqueous solution containing a surfactant to obtain an emulsion; and (2) A step of obtaining hollow microparticles by removing the dispersion medium and the solvent (B) from the emulsion obtained in the step (1). Includes:

[0035] The polymer solution contains a polymer (C) dissolved in a solvent (A) that is somewhat hydrophobic (logP or ClogP of 0.5 or greater), and also contains a solvent (B) with a boiling point higher than that of the solvent (A). Therefore, in step (1), the polymer solution is emulsified in an aqueous solution containing a surfactant to obtain an emulsion, resulting in a liquid-liquid core-shell phase-separated structure in which the shell contains the solvent (A) and the polymer (C) and the core contains the solvent (B). Furthermore, in step (2), hollow microparticles with a hollow core are obtained by removing at least the core solvent (B) in addition to the dispersion medium. Note that "removing" here does not necessarily mean completely removing the dispersion medium and solvent (B), but can also mean leaving some of them remaining, as long as the hollow microparticles are obtained. In the core-shell phase-separated structure described above, the solvent (A) may be contained in the swollen shell.

[0036] In step (1), a polymer solution containing solvent (A), solvent (B), and polymer (C) is emulsified to obtain a core-shell structure containing these three components. Therefore, none of the three components separate, forming a single phase. Such a single phase can be formed, for example, when solvent (A) and solvent (B) are compatible with each other, or when polymer (C) is soluble in both solvent (A) and solvent (B). The selection of these three components can be appropriately performed according to the above guidelines.

[0037] Thus, the manufacturing method of the present disclosure allows hollow microparticles to be produced without a polymerization reaction. When a polymerization reaction is performed during the hollow microparticle manufacturing process, the polymerization reaction must be carried out in a dispersion medium. Therefore, polymers that cannot undergo polymerization in a dispersion medium cannot be used. This problem is eliminated by the present disclosure, allowing the polymer design and particle design to be separated. This significantly increases the options for the type of polymer used in the shell. In other words, it is possible to separate the polymer design from the hollow particle design. Furthermore, because the process involves a liquid-liquid core-shell structure, the shape of the hollow microparticles approaches a perfect sphere with a single hole. Furthermore, the manufacturing method of the present disclosure also allows for control of the shape, number of holes, volume fraction, and film thickness. Furthermore, by controlling the amount of polymer, it is possible to create particles with depressions during the solvent removal process.

[0038] The surfactant is not particularly limited, and any known surfactant used for emulsion formation can be suitably used, such as polyvinyl alcohol and Pluronic (registered trademark) surfactants, which are block copolymers of polyethylene oxide and polypropylene oxide.

[0039] The type and concentration of the surfactant used affect the size of the core-shell structure. Specifically, a low surfactant concentration tends to result in a larger core-shell structure. The concentration of the surfactant in the aqueous solution is preferably 0.01 to 10 wt %, more preferably 0.1 to 3 wt %, based on the total weight (100 wt %) of the aqueous solution (aqueous solvent and surfactant).

[0040] The emulsification method is not particularly limited and can be widely applied. Examples of the emulsification method include membrane emulsification using a porous membrane such as Shirasu porous glass, mechanical emulsification using a homogenizer, and continuous emulsification in which these are handled continuously. The emulsification temperature can be freely selected within a range that does not exceed the boiling point of the solvent used in the emulsification environment.

[0041] As an emulsification method, membrane emulsification is preferred because it can obtain a more uniform core-shell structure. By passing through a more uniform core-shell structure, more uniform hollow microparticles can be more easily obtained by the production method of the present disclosure.

[0042] Examples of the membrane emulsification method include the following membrane emulsification method using a porous membrane. Step (i): A step of membrane-emulsifying the polymer solution (dispersed phase) into an aqueous solution (continuous phase) containing a surfactant through a porous membrane having uniform pore sizes to obtain an emulsion. Step (ii): A step of forming core-shell microparticles comprising a shell containing the polymer (C) and a core containing the solvent (B) by removing the solvent (A) contained in the emulsion.

[0043] In step (i), first, a polymer solution containing solvent (A), solvent (B), and polymer (C) is prepared as a dispersed phase. The thickness of the shell of the resulting core-shell structure can be controlled by adjusting the ratio of solvent (B) that forms the core to polymer (C) that forms the shell.

[0044] Next, the dispersion liquid prepared as the dispersed phase is forced through a porous membrane into a continuous phase containing a surfactant by applying pressure, for example, using nitrogen gas, to form a membrane emulsification. Specifically, the dispersed phase, which is an oil (O) layer, is forced through the porous membrane into the continuous phase, which is a water (W) phase, to form an O / W emulsion. The size of the formed emulsion is uniform (monodisperse) in correlation with the uniform pore size of the porous membrane. Furthermore, since the size of the formed emulsion is proportional to the pore size of the porous membrane, adjusting the pore size of the porous membrane makes it possible to control the size of the formed emulsion and, in turn, the size (particle size) of the microparticles. It is preferable to maintain the volume ratio of the dispersed phase to the continuous phase (dispersed phase / continuous phase) at 1 / 2 to 1 / 1000 (more preferably 1 / 5 to 1 / 100, and particularly preferably about 1 / 10).

[0045] The porous membrane is not particularly limited as long as it has uniform pore diameters, and various materials can be used, for example, those made of glass, resins such as polycarbonate, metals, etc. The pore diameter of the porous membrane can be determined depending on the desired size of the microparticles, but typically, a porous membrane having a pore diameter in the range of 0.05 to 20 μm (preferably 2 to 10 μm) can be used.

[0046] Furthermore, the membrane emulsification is preferably carried out under stirring in order to separate droplets from the membrane surface.

[0047] In step (ii), the solvent (A) in the emulsion obtained in step (i) is removed by evaporation. During the evaporation process, phase separation occurs into a shell component (O phase) containing the polymer (C), a core component (F phase) containing the solvent (B), and a continuous phase (W phase), forming core-shell particles having a shell containing the polymer (C) and a core containing the solvent (B).

[0048] In step (2), the solvent (B) is further removed from the core-shell structure in which the core encapsulates the solvent (B) in addition to the dispersion medium, thereby obtaining hollow microparticles.

[0049] In step (2), the method for removing the dispersion medium and solvent (B) from the emulsion is not particularly limited, and can be carried out by drying, for example. For example, natural drying makes it difficult to remove solvent (B) from the cores, so it is preferable in terms of efficiency to adopt a drying method that more easily removes solvent (B). Such drying methods are preferably forced drying methods rather than natural drying, and examples include freeze drying, heat drying, vacuum drying, and reduced-pressure drying. Note that even when natural drying is used, it is possible to remove solvent (B) from the cores by adjusting conditions such as temperature and / or humidity, or by using a longer drying time.

[0050] As for the freeze-drying conditions, it is preferable to reduce the pressure to near vacuum, which lowers the boiling points of the coexisting water and solvent, and more preferable to set conditions that allow the solvent to sublimate in order to prevent destruction of the hollow particles due to expansion of the core liquid. Such conditions can be appropriately set depending on the type of solvent, etc.

[0051] In the manufacturing method of the present disclosure, the water, surfactant, and the like contained in the starting materials can be removed after step (1) or after step (2). For example, when removed after step (1), the water, surfactant, and the like are present as a continuous phase outside the core-shell structure. In this case, the method for removing this continuous phase is not particularly limited and can be appropriately selected depending on the relationship between the continuous phase and the core-shell structure, etc. For example, if the core is sufficiently hydrophobic, the continuous phase can be easily removed. On the other hand, if the core is relatively hydrophilic and the surface of the core is swollen with water, it can be removed by drying. If water and surfactant remain after step (2), they can be removed by the same method as described above.

[0052] The polymer (C) may be used alone or in combination of two or more.

[0053] The polymer (C) may be any polymer soluble in the solvent (A), and the structure is not particularly limited. Since hollow microparticles can be formed as long as the polymer is dissolved in the solvent (A) and then solidified by drying, the structure is not necessarily limited. Furthermore, since the polymer (C) forms the structure of the hollow microparticles, it must have physical properties that allow the structure to be maintained. Specifically, it must have a melting point of 70°C or higher, preferably 80°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher. Additionally, it must have a glass transition point of 120°C or higher, preferably 130°C, more preferably 140°C, and even more preferably 150°C or higher.

[0054] The type of polymer (C) is not particularly limited, but can be selected from a wide range of polymers synthesized by chain polymerization, step-growth polymerization, or living polymerization, as long as it satisfies the above-mentioned solvent solubility. These may be copolymers, and are not particularly limited, and any of random copolymerization, alternating copolymerization, block copolymerization, and graft copolymerization can be used.

[0055] Chain polymerization is a reaction in which active species obtained from a monomer react with another monomer to grow a molecular chain. Specific examples include radical polymerization, anionic polymerization, cationic polymerization, coordination polymerization, and ring-opening polymerization. Examples of polymers include vinyl polymers, acrylic polymers, nylon polymers, and cycloolefin polymers. Examples of polymers include polystyrene, polymethyl methacrylate, polyvinyl halide, fluorinated vinyl monomer (such as tetrafluoroethylene)-vinyl monomer (such as vinyl acetate or vinylpyrrolidone) copolymers, and Zeonex manufactured by Zeon Corporation.

[0056] Sequential polymerization is a reaction in which a molecular chain grows by bonding between reactive points of monomers, and specific examples include polycondensation, addition condensation, etc. Examples of polymers include polyamide, polyetherimide, polyimide, polyamideimide, polyester, polycarbonate, polyaryletherketone, polysulfone, polyethersulfone, phenolic resin, etc.

[0057] A condensation polymer refers to a polymer synthesized by repeated condensation or addition between bifunctional compounds, and reactions used for the synthesis include, for example, polycondensation reaction, polyaddition reaction, polyaddition-condensation reaction, etc. In the present disclosure, in terms of the physical properties of the resulting hollow microparticles, it is preferable to use a condensation polymer as polymer (C) because it has excellent mechanical properties.

[0058] Examples of the homopolymer include acrylic polymers.

[0059] As for the homopolymer and copolymer, the main chain preferably contains one or more groups selected from the group consisting of ethers and ketones; or a cyclic structure.

[0060] The copolymer polymer (C) may be any of an alternating copolymer, a random copolymer, a block copolymer and a graft copolymer.

[0061] Examples of the cyclic structure include aromatic rings such as benzene rings and non-aromatic rings such as cyclohexane, which may have one or more substituents. Examples of the non-aromatic ring include aliphatic 4- to 12-membered rings, preferably aliphatic 4- to 7-membered rings. More specific examples include pyrrolidone.

[0062] Examples of the substituent include halogen atoms such as fluorine atom, chlorine atom, bromine atom, and iodine atom, hydroxyl group, mercapto group, amino group, nitro group, cyano group, etc. The number of substituents is, for example, one or more up to the maximum number possible for substitution (e.g., two, three, four, or five).

[0063] Examples of the polymer (C) that is a homopolymer include polyphenylene ether, polyacetal, and cycloolefin polymer.

[0064] The condensation polymer preferably has a main chain containing one or more groups selected from the group consisting of amide, imide, ester, sulfonyl, and sulfone.

[0065] Examples of the polymer (C) that is a condensation polymer include polyamide, polyetherimide, polyimide, polyamideimide, polyester, polycarbonate, polyaryletherketone, polysulfone, polyethersulfone, polycaprolactone, and polycaprolactam.

[0066] The polymer (C) which is a condensation polymer is preferably polyamide, polyetherimide, polyimide, polyamideimide, polyester, or polycarbonate.

[0067] In particular, polyimide is preferred as the polymer (C) which is a condensation polymer.

[0068] Specific examples of condensation polymers include fluorine-containing polyimides such as 4,4'-[perfluoropropane-2,2'-diyl]diphthalic anhydride / 2,2'-bis(trifluoromethyl)-4,4'diaminobiphenyl alternating copolymer, solvent-soluble polyimides and polyamides such as KPI-MX300F manufactured by Kawamura Sangyo and Spixeria manufactured by Somar, solvent-soluble polycarbonates such as Iupizeta manufactured by Mitsubishi Gas Chemical Company, Inc., and solvent-soluble polyesters such as Vylon manufactured by Toyobo MC Co., Ltd.

[0069] Examples of polyamides include aliphatic polyamides, semi-aromatic polyamides, and aromatic polyamides.

[0070] Examples of polyimides include polyimides containing the following structures as repeating units. [ka] (In the formula, R 1 represents an aromatic ring structure, and R 1 each forms a ring of 5 or 6 atoms with the adjacent imide group. R 1 is not particularly limited as long as it can ensure solvent solubility, but may be any of the following formulas: [ka] It is preferable that Rf 1~2 are the same or different and represent a perfluoroalkyl group having 1 to 10 carbon atoms). R 2 is NH2-R 2 represents the carbon chain portion of a diamine represented by —NH2, where n is an integer of 1 or more.

[0071] R2 is not particularly limited, but is a fluorine-containing alkyl chain having 1 to 30 carbon atoms, which may be branched or may contain an ether functional group in the main chain. 2 The internal structure may contain multiple repeat units.

[0072] Examples of polyesters include polycaprolactone (PCL) and polylactic acid (PLA). Polyhydroxybutyrate (PHB), Polyglycolic acid (PGA), Polyethylene adipate (PEA), Polyethylene terephthalate (PET), Polybutylene terephthalate (PBT) Polyethylene naphthalate (PEN), polytrimethylene terephthalate (PTT), polyester of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid (LCP), polyester of bisphenol A and phthalic acid (PAR), etc. can be used.

[0073] In order for the polymer (C) to be easily dissolved in the solvent (A) while maintaining its mechanical properties, the molecular weight of the polymer (C) is preferably 1,000 to 1,000,000, more preferably 1,500 to 500,000, and even more preferably 2,000 to 100,000. In practice, a soluble polymer (C) can be appropriately selected depending on the type of solvent (A).

[0074] Depending on the function to be imparted to the resulting hollow microparticles, the polymer (C) can be, for example, a fluorine-containing polymer. In this case, due to the low intermolecular attractive force and low surface free energy of the fluorine-containing polymer, the hollow microparticles of the present disclosure can be dispersed in an aqueous medium. Furthermore, fluorine-containing polymers have excellent stability against acids, alkalis, and hot water, and also have excellent long-term stability in water. Furthermore, they have the advantage of providing a smooth surface that reduces microbial growth. Therefore, the type of fluorine-containing polymer is not particularly limited. For example, fluorine atoms may be contained in part of the various polymers described above.

[0075] The boiling point of the solvent (A) at room temperature and normal pressure is preferably 150°C or lower, more preferably 130°C or lower, and even more preferably 100°C or lower.

[0076] The logP or ClogP of the solvent (A) is preferably 1-3.

[0077] Log P is a physical property that indicates the hydrophobicity of a molecule. Specifically, when a compound is dissolved in a mixture of water and 1-octanol and reaches equilibrium, the concentration ratio of the two is the partition coefficient, P = C. 1-octanol / C water It is quantified as the common logarithm of octanol. Octanol is thought to be similar in nature to biological membranes, whose hydroxyl groups have the same hydrogen bond donating and accepting capabilities. The higher this value, the more hydrophobic the substance is, i.e., the more lipophilic it is.

[0078] ClogP is one of the predicted values ​​of LogP, and can be determined by experimental measurement or calculation. In principle, the LogP value of a molecule is essentially additive, so parameters for each substituent are determined based on a large number of measured values, and the value for the entire molecule is predicted. Furthermore, parameters related to intramolecular interactions (e.g., intramolecular hydrogen bonds, steric effects, etc.), which are factors that disrupt additivity, are also supplemented. The latest version also includes a function to predict parameters even for substituents without parameters, making it possible to generate predicted values ​​for any given structure. When performing estimation, commercially available parameter prediction software can be used; in this disclosure, the chemoinformatics library "RDKit" is used.

[0079] The solvent (A) may be used alone or in combination of two or more. In the case of a mixed solvent, the ClogP of the mixed solvent as a whole is preferably 0.5 or more and within the above-mentioned preferred range. The mixed solvent referred to here is a solvent in which two or more solvents are mixed in amounts that clearly exceed the level generally considered to be impurities (generally on the order of ppm).

[0080] Preferred examples of the solvent (A) include aprotic polar solvents, nonpolar solvents, low-polarity solvents, alcoholic solvents, and fluorine-based solvents. Examples of aprotic polar solvents include N,N-dimethylformamide, acetonitrile, dimethyl sulfoxide, hexamethylphosphoric triamide, N-methylpyrrolidone, ethyl acetate, dimethyl carbonate, acetone, methyl ethyl ketone, tetrahydrofuran, and dioxane. Examples of nonpolar solvents include carbon tetrachloride, benzene, toluene, hexane, and cyclohexane. Examples of low-polarity solvents include diethyl ether, monoglyme, dichloromethane, and chloroform. Examples of alcoholic solvents include methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, glycerin, and mannitol. Examples of fluorine-based solvents include hydrofluoroethers such as perfluorohexane, perfluorobenzene, and methoxynonafluorobutane, perfluorocrown ethers, 1-bromoheptadecafluorooctane, 1-bromotridecafluorohexane, perfluorodecalin, hexafluoroisopropanol, and 2-perfluorohexylethanol.

[0081] When solvent (A) is a single solvent, its logP or ClogP must be 0.5 or greater. Such a solvent can be appropriately selected from the solvent group described above. For example, nonpolar solvents and low-polarity solvents can be used alone. In addition, ethyl acetate, dichloromethane, chloroform, perfluorohexane, perfluorobenzene, hydrofluoroethers such as methoxynonafluorobutane, 1-bromoheptadecafluorooctane, 1-bromotridecafluorohexane, perfluorodecalin, hexafluoroisopropanol, and 2-perfluorohexylethanol can also be used alone.

[0082] The solvent (B) may be used alone or in combination of two or more. In the case of a mixed solvent, the solvent (B) has a higher boiling point than the solvent (A) as a whole mixed solvent.

[0083] When solvent (B) is a single solvent, it is not particularly limited as long as it has a boiling point higher than that of solvent (A). The difference in boiling point between solvent (B) and solvent (A) is preferably 10 to 200°C, more preferably 30 to 180°C, and even more preferably 40 to 150°C.

[0084] Examples of the solvent (B) include fluorocarbons. In the present disclosure, "fluorocarbon" refers to an organic fluorine compound having a carbon-fluorine bond. Examples of fluorocarbons include perfluorooctyl bromide, perfluorodecalin, perfluoromethyldecalin, perfluorooctane, perfluorononane, perfluorodecane, perfluorododecane, perfluorotridecane, perfluorotributylamine, perfluorobutyltetrahydrofuran, and perfluoroadamantane.

[0085] It is preferable that solvent (B) be more hydrophobic than solvent (A), i.e., have a higher logP or ClogP, in order to facilitate the formation of a core-shell structure in step (1). Because an aqueous emulsion is obtained in step (1), if solvent (B) is more hydrophobic than solvent (A), solvent (B) is more likely to be oriented toward the core. In particular, when the boiling point difference between solvent (A) and solvent (B) is smaller, solvent (B) tends to be less likely to be oriented toward the core. In this case, it is more preferable that solvent (B) be more hydrophobic than solvent (A). The combination of solvent (A) and solvent (B) can be appropriately determined according to the above guidelines.

[0086] hollow particles The hollow microparticles of the present disclosure are hollow microparticles whose shells contain a polymer that is soluble in a solvent and has a logP or ClogP of 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more.

[0087] The hollow microparticles of the present disclosure can be obtained by the method for producing hollow microparticles of the present disclosure.

[0088] As mentioned above, the method for producing hollow microparticles of the present disclosure has the advantage that hollow microparticles can be produced without a polymerization reaction. Because the hollow microparticles of the present disclosure are obtained by this production method, the polymers (C) in the shell are not crosslinked to each other, or the degree of crosslinking is lower than that of those obtained by conventional production methods involving polymerization reactions. Therefore, the shells obtained by conventional production methods involving polymerization reactions cannot be dissolved in solvents with a logP or ClogP of 0.5 or higher because the polymers are crosslinked to each other. However, the hollow microparticles of the present disclosure can dissolve their shells in the above solvents. Therefore, the hollow microparticles of the present disclosure have the advantage that the polymers dissolved as described above can be reused to reconstitute the hollow microparticles of the present disclosure.

[0089] The hollow fine particles of the present disclosure preferably have an average particle diameter of 1 μm to 50 μm, more preferably 2 μm to 45 μm, and even more preferably 3 μm to 40 μm.

[0090] In the present disclosure, the average particle size of hollow fine particles means the number average particle size, which is measured as follows: It can be measured using a laser diffraction particle size distribution measuring device or the like.

[0091] The shell thickness of the hollow microparticles of the present disclosure may be any thickness that does not exceed the particle radius, and is preferably 0.01 μm to 20 μm, more preferably 0.02 μm to 19 μm, and even more preferably 0.03 μm to 17 μm. In the present disclosure, the shell thickness of hollow microparticles is measured as follows: the resulting particles are cut and observed under a scanning electron microscope to obtain the thickness.

[0092] The hollow microparticles of the present disclosure preferably have a volume fraction of 30% to 99%, more preferably 35% to 95%, and even more preferably 40% to 90%. The shape of the voids is not particularly limited, but may be spherical, ellipsoidal, rod-shaped, or ant nest-shaped. Furthermore, in the case of hollow microparticles prepared via emulsification, preferably 50% or more, more preferably 70% or more, and even more preferably 80% or more of the voids are spherical. In the present disclosure, the volume fraction of hollow microparticles is calculated as follows: The void volume can be calculated from the measured film thickness and particle diameter, and the volume fraction can be calculated by calculating the ratio to the spherical volume. Furthermore, in this method, the particles obtained are nearly spherical, and the film thickness is nearly uniform due to the emulsification process. Therefore, the volume fraction can be approximately calculated from the amounts of polymer (C) and solvent (B) used.

[0093] The hollow microparticles of the present disclosure are obtained by the production method of the present disclosure, and are therefore obtained via a liquid-liquid core-shell structure, and therefore the hollow microparticles of the present disclosure are preferably spherical.

[0094] For the same reasons as above, the hollow microparticles of the present disclosure preferably have one or two voids.

[0095] Since the hollow microparticles of the present disclosure are obtained by the manufacturing method of the present disclosure, a more uniform population of hollow microparticles can be obtained, as described above, by employing, for example, membrane emulsification as an emulsification method. In this case, the population of hollow microparticles of the present disclosure can have a monodisperse particle size distribution. Specifically, the CV value of the population of hollow microparticles of the present disclosure is preferably 70% or less, more preferably 40% or less, even more preferably 35% or less, and even more preferably 30% or less. In the present disclosure, the CV value of a population of hollow microparticles is the coefficient of variation of the particle size distribution, calculated from the standard deviation of particle diameters and the volume-average particle diameter. A lower CV value indicates better particle diameter uniformity. Specifically, the coefficient of variation of the particle size distribution, CV, can be calculated using the following formula: CV value (%) = (standard deviation of particle size / volume average particle size) x 100

[0096] The hollow microparticles of the present disclosure are obtained by the manufacturing method of the present disclosure and may contain trace amounts of some of the raw materials used in the manufacturing method of the present disclosure. In this case, the hollow microparticles of the present disclosure contain a total of: (A) at least one solvent with a logP or ClogP of 0.5 or more; and / or (B) at least one solvent with a boiling point higher than that of solvent (A) on the surface and interior of the shell and in the core, in an amount of 0% to 1% by weight, preferably more than 0% by weight and 1% by weight or less, more preferably 0.5% by weight or less, and even more preferably 0.1% by weight or less. In this numerical range, "more than 0% by weight" means that the substance is detected at a concentration exceeding the detection limit of the measurement method used.

[0097] The hollow particles of the present disclosure are considered to have excellent low dielectric properties due to their hollow structure, and are therefore suitable for use in electrical materials, including, but not limited to, printed wiring boards, antenna substrates, and interlayer insulating films for high-frequency connectors.

[0098] The hollow microparticles of the present disclosure are believed to have excellent low refractive index due to their hollow structure, and can be applied to various applications requiring a low refractive index. That is, the hollow microparticles of the present disclosure can be used as low refractive index materials. When used as low refractive index materials, they can be suitably used, for example, in antireflection films, refractive index adjusters, fillers added to optical adhesives, low refractive index lens materials, prisms, and sensitizers for radiation therapy.

[0099] The hollow particles of the present disclosure can be lightweight because they are hollow, and therefore can be applied to various applications where weight reduction is required. That is, the hollow particles of the present disclosure can be used as a metal replacement material for automobiles. Furthermore, since the hollow particles contain air, they have excellent heat insulating properties and are suitable for use as heat insulating materials.

[0100] The hollow particles disclosed herein are believed to be capable of encapsulating substances because they are hollow, and are therefore applicable to a variety of substance-absorbing applications. That is, the hollow microparticles disclosed herein can be suitably used as adsorbents such as desiccants, carriers for catalysts, pharmaceutical carriers used in drug delivery systems, nanoparticle-encapsulated sensors, and the like.

[0101] The hollow particles of the present disclosure are hollow and therefore contain air at low density, and therefore can be applied to applications requiring weight reduction and thermal insulation. That is, the hollow fine particles of the present disclosure can be suitably used as resin fillers for weight reduction, thermal insulation materials, and thermal insulation applications. [Example]

[0102] The present disclosure is not limited to the following examples.

[0103] Example 1 (Step 1) 50 mg of 4,4'-[perfluoropropane-2,2'-diyl]diphthalic anhydride / 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl alternating copolymer (fluorine content 33 wt%) and 0.12 g of perfluorooctyl bromide were dissolved in 2 mL of dichloromethane (logP = 1.25). Nile red was added for fluorescence measurement. The resulting solution was then extruded with a syringe through a hydrophilic glass porous membrane into 20 mL of 2% aqueous polyvinyl alcohol solution, resulting in membrane emulsification and emulsion particles.

[0104] (Step 2) Subsequently, the dichloromethane and perfluorooctyl bromide were evaporated at room temperature while stirring the emulsion, yielding hollow microparticles composed of 4,4'-[perfluoropropane-2,2'-diyl]diphthalic anhydride / 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl alternating copolymer. The volume average particle size was 6.63 μm. The CV value was 29%.

[0105] Comparative Example 1 Emulsification was carried out in the same manner as in Example 1, except that 2 mL of acetone (logP=-0.24) was used as the solvent. However, because acetone was dissolved in the aqueous solution, emulsified particles, which are precursors of hollow microparticles, could not be formed.

Claims

1. （１） (A) at least one solvent having a log P or Clog P of 0.5 or greater; (B) at least one solvent having a boiling point higher than that of the solvent (A); and (C) at least one polymer that is soluble in the solvent (A); in an aqueous solution containing a surfactant to obtain an emulsion; and （２） A step of obtaining hollow microparticles by removing the dispersion medium and the solvent (B) from the emulsion obtained in the step (1). A method for producing hollow microparticles, comprising:

2. 2. The method for producing hollow microparticles according to claim 1, wherein in the step (2), hollow microparticles are obtained via a core-shell structure in which the solvent (B) is contained in the core and the polymer (C) is contained in the shell.

3. 3. The method for producing hollow microparticles according to claim 1, wherein in the step (2), the dispersion medium and the solvent (B) are removed by freeze-drying, heat drying, or vacuum drying.

4. The main chain of the polymer (C) is: one or more groups selected from the group consisting of siloxane, amide, imide, ester, ether, sulfonyl, sulfone, and ketone; or Ring structure The method for producing hollow microparticles according to claim 1 or 2, comprising:

5. 3. The method for producing hollow microparticles according to claim 1, wherein the polymer (C) is at least one polymer selected from the group consisting of polydialkylsiloxane, polyphenylene ether, polyamide, polyetherimide, polyimide, polyamideimide, polyester, polycarbonate, polyacetal, polyaryletherketone, polysulfone, polyethersulfone, and cycloolefin polymer.

6. 3. The method for producing hollow microparticles according to claim 1, wherein the polymer (C) is polydimethylsiloxane or polyimide.

7. 3. The method for producing hollow microparticles according to claim 1, wherein the boiling point of the solvent (A) at room temperature and normal pressure is 100°C or lower.

8. 3. The method for producing hollow microparticles according to claim 1, wherein the solvent (A) has a log P or C log P of 1 to 3.

9. 3. The method for producing hollow microparticles according to claim 1, wherein the solvent (A) is at least one solvent selected from the group consisting of fluoroethers, chloroform, and dichloromethane.

10. 3. The method for producing hollow microparticles according to claim 1, wherein the solvent (B) is a perfluorocarbon.

11. Hollow microparticles, the shell of which comprises a polymer that is soluble in a solvent having a log P or C log P of 0.5 or greater.

12. The backbone of the polymer is: one or more groups selected from the group consisting of amide, imide, ester, ether, sulfonyl, sulfone, and ketone; or Ring structure The hollow microparticle of claim 11, comprising:

13. 13. The hollow microparticle according to claim 11, wherein the polymer is at least one polymer selected from the group consisting of polydialkylsiloxane, polyphenylene ether, polyamide, polyetherimide, polyimide, polyamideimide, polyester, polycarbonate, polyacetal, polyaryletherketone, polysulfone, polyethersulfone, and cycloolefin polymer.

14. 13. The hollow microparticle according to claim 11, wherein the polymer is at least one polymer selected from the group consisting of polyester, polyamide, polyamideimide, polyimide, polyetherimide, and polycarbonate.

15. 13. The hollow microparticle according to claim 11 or 12, wherein the polymer is polydimethylsiloxane or polyimide.

16. 13. The hollow microparticle according to claim 11, wherein the boiling point of the solvent at room temperature and normal pressure is 100°C or lower.

17. 13. The hollow microparticle according to claim 11, wherein the solvent has a log P or C log P of 1 to 3.

18. 13. The hollow microparticle according to claim 11, wherein the solvent is at least one solvent selected from the group consisting of fluoroethers, chloroform, and dichloromethane.

19. The hollow microparticles according to claim 11 or 12, having an average particle diameter of 1 μm to 50 μm.

20. 13. The hollow microparticle according to claim 11, wherein the shell has a thickness of 0.01 μm to 20 μm.

21. 13. The hollow microparticle according to claim 11, wherein the volume fraction of the shell layer constituting the particle is 50% or less.

22. 13. The hollow microparticle according to claim 11 or 12, wherein the number of voids in the particle is 1 or 2.

23. On the surface and inside of the shell and in the core in total: (A) at least one solvent having a log P or C log P of 0.5 or greater; and / or (B) at least one solvent having a boiling point higher than that of the solvent (A); The hollow microparticle according to claim 11 or 12, wherein the total of:

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